WO2016179667A1

WO2016179667A1 - An internal combustion engine powered multi-rotor aircraft and methods of control thereof

Info

Publication number: WO2016179667A1
Application number: PCT/AU2016/050367
Authority: WO
Inventors: Seppo Saario
Original assignee: Seppo Saario
Priority date: 2015-05-14
Filing date: 2016-05-14
Publication date: 2016-11-17

Abstract

There is provided a multirotor aircraft comprising a platform; and at least two pairs of opposing radial arms extending from the platform, the radial arms supporting at least four internal combustion engine powered rotors, rotating actuators for rotating each of the radial arms about an elongate axis; and a flight controller configured for controlling the rotating actuators, wherein the rotors rotate in the same direction; and the flight controller is configured for yaw control by controlling the rotating actuators to rotate at least one pair of the opposing radial arms in opposing rotational directions.

Description

AN I NTERNAL COM BUSTION ENG I N E POWERED M U LTI-ROTOR AI RCRAFT AN D M ETHODS OF CONTROL TH E REOF

Field of the Invention

[I] The present invention relates to multi-rotor aircraft and in particular, but not necessarily entirely, to an internal combustion engine powered multi-rotor aircraft and methods of control thereof.

Background of the Invention

[2] Figure 2 shows a quad multirotor 9 abstraction in accordance with the prior art, commonly referred to as a quad copter.

[3] As can be seen, the quad multirotor 9 comprises a platform 8 having radial arms 4 extending therefrom supporting four rotors 3 driven by electric motor.

[4] As can be seen, adjacent rotors rotate in opposing directions. In this manner, yaw control is achieved by adjusting power selectively to favour rotors rotating in a certain direction and therefore to rotate the platform 8 accordingly.

[5] Specifically, as can be seen, opposing rotors Al and A2 rotate clockwise whereas opposing rotors Bl and B2 rotate counterclockwise.

[6] As such, to rotate the platform 8 clockwise, power would be increased to motors Bl and B2 (which may include decreasing power to rotors Al and A2) such that the direction of motion of rotors Bl and B2 turns the platform 8 clockwise.

[7] Similarly, to rotate counterclockwise, power would be increased to rotors Al and A2 which may similarly include decreasing power to rotors Bl and B2.

[8] However, a need exists for multirotor platforms having extended flight times, greater payload capacities and the like. As such, it is desirable to utilise internal combustion engines given the superior engine density of their fuel as compared to battery storage.

[9] Existing large-scale multirotor platforms, such as the Boeing CH-47 Chinook utilise counter- rotating rotors including for yaw control.

[10] However, for smaller platform it is difficult to implement counter-rotating rotors on account of the difficult and unfeasible mechanical modifications required for internal combustion engines as opposed to electric motors for which the voltage or phases for a brushless motor may simply be reversed.

[II] Furthermore, horizontal transitioning of conventional multirotor platforms comprises differential power supply to opposing rotors so as to adjust the pitch of the platform so as to cause the platform to transition horizontally in the direction pitched. [12] However, travelling at a pitched angle increases the horizontal cross-sectional surface area thereby increasing wind resistance and decreasing flight efficiency. Furthermore, the relative airflow incident on the upper surface of the platform results in a downward force on the platform which must be countered by the rotors.

[13] The present invention seeks to provide an internal combustion engine powered multi-rotor aircraft and methods of control thereof, which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.

[14] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.

Summary of the Disclosure

[15] In accordance with one aspect, there is provided a multirotor aircraft comprising: a platform; and at least two pairs of opposing radial arms extending from the platform, the radial arms supporting at least four internal combustion engine powered rotors; rotating actuators for rotating each of the radial arms about an elongate axis; and a flight controller configured for controlling the rotating actuators, wherein: the rotors rotate in the same direction; and the flight controller is configured for yaw control by controlling the rotating actuators to rotate at least one pair of the opposing radial arms in opposing rotational directions.

[16] The flight controller may be configured for yaw control by controlling the rotating actuators to rotate at least two pairs of the opposing radial arms in opposing rotational directions.

[17] The flight controller may be configured for horizontal transition control by controlling the rotating actuators to rotate at least one pairs of the opposing radial arms in the same rotational directions.

[18] The flight controller may be configured for horizontal transition control by controlling the rotating actuators to rotate at least two pairs of the opposing radial arms in the same rotational directions.

[19] The flight controller may be configured for horizontal transition control by controlling the rotating actuators to rotate each of the at least two pairs of the opposing radial arms to differing rotational offsets.

[20] The differing rotational offsets are determined by the flight controller in accordance with a desired direction of travel.

[21] The at least two pairs of opposing radial arms are three pairs of radial arms.

[22] The at least two pairs of opposing radial arms are four pairs of radial arms. [23] The flight controller may be configured for roll and pitch control by controlling throttle setpoints of opposing rotors of at least one pair of the radial arms.

[24] The flight controller may be configured for roll and pitch control by controlling throttle setpoints of opposing rotors of at least two pairs of the radial arms.

[25] At least one of the radial arms may comprise a hybrid lift flight surface.

[26] The flight surface may be substantially planar and horizontally orientated.

[27] The flight surface may be configured to pitch in a direction opposite to a direction of rotation the at least one radial arm.

[28] Each flight surface has a corresponding mechanical linkage to the respective radial arm to pitch the flight surface.

[29] The flight controller may be configured for controlling the pitch of the platform by controlling a throttle setpoint of at least one of fore and aft rotors.

[30] The multirotor aircraft may further comprise flight surfaces operably coupled to each arm, each flight surfaces having an associated actuator for pitching the flight surface about the elongate axis of the associated arm and for being controlled by the controller and wherein the flight controller is configured for controlling the pitch of the platform by controlling the pitch of at least one of the flight surfaces.

[31] The flight controller may be configured for controlling the pitch of the platform by pitching a fore flight surfaces substantially vertically so as to reduce lift generated by the fore flight surfaces.

[32] The flight controller may be configured for controlling the pitch of the platform by pitching an aft flight surfaces substantially horizontally so as to maintain lift generated by the aft flight surfaces.

[33] The flight controller may be configured for engine failure monitoring.

[34] Engine failure monitoring may comprise monitoring an engine response to a throttle setpoint.

[35] Monitoring the engine response may comprise monitoring the revolution speed of a propeller shaft of each internal combustion engine.

[36] Monitoring the engine response may comprise determining whether the revolution speed falls within a bound specified for a particular throttle setpoint.

[37] Monitoring the engine response may comprise determining the rate of change of the revolution speed.

[38] Monitoring the engine response may comprise determining whether the rate of change of the revolution speed falls within rate of change bounds. [39] Engine failure monitoring may comprise detecting an engine failure and controlling a throttle setpoint of an opposing rotor.

[40] Other aspects of the invention are also disclosed.

Brief Description of the Drawings

[41] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[42] Figure 1 shows an exemplary internal combustion engine powered multirotor in a hex copter configuration in accordance with an embodiment of the present disclosure;

[43] Figure 2 shows a quad copter abstraction in accordance with the prior art;

[44] Figure 3 shows a quad copter abstraction in accordance with an embodiment of the present disclosure;

[45] Figure 4 shows a hex copter abstraction in accordance with an embodiment of the present disclosure;

[46] Figure 5 shows a quad copter abstraction comprising hybrid lift generation flight surfaces in accordance with an embodiment of the present disclosure; and

[47] Figure 6 shows a functional schematic of a flight controller in accordance with an embodiment of the present disclosure.

Description of Embodiments

[48] For the purposes of promoting an understanding of the principles in accordance with the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the disclosure as illustrated herein, which would normally occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the disclosure.

[49] Before the structures, systems and associated methods relating to an internal combustion engine powered multi-rotor aircraft and methods of control thereof are disclosed and described, it is to be understood that this disclosure is not limited to the particular configurations, process steps, and materials disclosed herein as such may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the disclosure will be limited only by the claims and equivalents thereof. [50] In describing and claiming the subject matter of the disclosure, the following terminology will be used in accordance with the definitions set out below.

[51] It must be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[52] As used herein, the terms "comprising," "including," "containing," "characterised by," and grammatical equivalents thereof are inclusive or open-ended terms that do not exclude additional, unrecited elements or method steps.

[53] It should be noted in the following description that like or the same reference numerals in different embodiments denote the same or similar features.

[54] Turning to figure 1, there is shown a hex copter 1 in accordance with an embodiment of the present disclosure. As can be seen, the hex copter 1 is powered by internal combustion engines 2.

[55] Specifically, the hex copter 1 comprises a platform 8 from which radial arms 4 extend radially therefrom. The distal end of each radial arm 4 supports the internal combustion engine 2.

[56] Each internal combustion engine 2 powers a rotor 3 so as to produce a lift.

[57] The platform 8 housing supports the requisite electronics for flight control, fuel supply and the like. The flight control may comprise redundant systems, such as redundant power supplies, power buses and the like for increased reliability. The housing may be supported by a plurality of legs 7 which may comprise suspension for shock absorption purposes.

[58] Whereas the exemplary embodiment of figure 1 shows a hex copter configuration, it should be appreciated that other configurations are equally applicable within the purposive scope of the embodiments described herein including quad copter and octo copter configurations.

[59] Turning now to figure 3, there is shown an abstraction of a quad copter 22 in accordance with an embodiment to illustrate flight control utilising internal combustion engines.

[60] As can be seen, in this embodiment, the quad copter 22 comprises four rotors powered by internal combustion engine.

[61] For illustrative convenience, the rotors comprise a first pair of opposing rotors Al and A2 and a second pair of opposing rotors Bl and B2.

[62] For reference purposes, direction of travel through 360° will be described wherein 0° corresponds with rotor Al, 90° with rotor B2 and so on.

[63] Now, as can be seen, all of the rotors rotate in the same direction, shown as clockwise in the embodiment provided. Such an arrangement negates the need for mechanical modification of the internal combustion engines 2.

[64] However, yaw control cannot be achieved in the same manner as for conventional arrangements relying on counter-rotating rotors. [65] As such, so as to achieve yaw control, as can be seen, each radial arm 4 is able to rotate about the elongate axis.

[66] Specific, the platform 8 comprises a plurality of rotating actuators for each of the radial arms 4 so as to be able to rotate the radial arms accordingly, such as to a specific setpoint as determined by the flight controller.

[67] In embodiments, the rotating actuators may comprise servos controlled by the flight controller but other activating arrangements may be utilised within the purposive scope of the embodiments described herein.

[68] Returning again to figure 1, as can be seen, each radial arm 5 may have a rotation lim iting device 5 fastened adjacent each arm 4 within which a perpendicular pin travels so as to mechanically limited the rotational extent of each radial arm 4.

[69] Returning again to figure 3, in order to achieve yaw control, the flight controller 11 would cause the rotating actuators to rotate at least one pair of opposing arms 4 in opposing rotational directions.

[70] Specifically, and with reference to figure 3, should the flight controller wish to rotate the platform 8 clockwise, the flight controller 11 would rotate the opposing radial arms in opposing rotational directions by controlling a rotating actuator to rotate the arm of rotor Bl to pitch rearwards (with reference to the A1-A2 axis) and rotate the arm of rotor B2 to pitch forwards such that the platform 8 would rotate.

[71] Ideally, during yaw control, opposing radial arms are rotated in opposing directions. However, in embodiments, a single radial arm 4 may be rotated depending on the application.

[72] In further embodiments, more than one opposing pair of radial arms 4 may be rotated. Again, with reference to figure 3, while the radial arms of rotors Bl and B2 are rotated in the manner described above, the radial arms 4 of rotors Al and A2 may be simultaneously rotated in opposing directions.

[73] Turning now to figure 4, there is shown an abstraction of a hex copter 23. As can be seen in this embodiment, the hex copter 23 comprises three pairs of opposing radial arms 4. As such, yaw control would be achieved in a similar manner described above wherein at least one opposing pair of radial arms would be rotated by the flight controller in opposing directions so as to rotate the platform accordingly. Yet further, all three pairs of opposing radial arms may be rotated in opposing manners such that all rotors contribute to yaw control of the platform 8.

[74] In embodiments, the rotational offset each radial arm 4 may be set by the flight controller 11 [75] Roll and pitch control may be achieved by the flight controller substantially in accordance with conventional arrangements through varying the speed of the respective rotors.

[76] Specifically, turning now to figure 6, there is shown the flight controller 11 comprising a pulse with modulator output 18 for controlling corresponding throttle control 20 of each internal combustion engine 2.

[77] As such, and referring again to figure 3, in order to control the pitch of the quad copter 22, the flight controller 11 would increase the throttle setting of rotor A2 and, in embodiments, simultaneously decrease the throttle setting of opposing rotor Al so as to cause the platform 8 to pitch forwards.

[78] Similarly, the roll of the platform 8 may be adjusted in this way also.

[79] As alluded to above, horizontal transition for conventional arrangements is achieved by yaw and pitch control. However, travelling at a pitched angle increases the horizontal cross-sectional surface area thereby increasing drag and induces a downward force on the platform, reducing efficiency.

[80] Now, conversely, horizontal transition control in accordance with present embodiments is achieved again by rotating the radial arms 4.

[81] Specifically, turning to figure 3, the flight controller 3 would transition the platform 8 horizontally in a 0° direction by simultaneously rotating the radial arms 4 of rotors Bl and B2 in the same direction so as to cause rotors Bl and B2 to pitch forwards (with reference to the Al - A2 axis).

[82] As such, to travel on a 0° direction, both rotors Bl and B2 would be pitched forwards through the rotation of the radial arms 4 whereas rotors Al and A2 would remain unaffected.

[83] In embodiments, the perpendicular angle of the rotor axle with respect to the radial arm 4 may additionally be controllable such that as the radial arms 4 of rotors Bl and B2 rotate to pitch these rotors forwards, rotors Al and A2 are simultaneously tilted forwards.

[84] Similarly, to transition the platform 22 in a 90° direction, the radial arms 4 of rotors Al and A2 would similarly be rotated in the same direction so as to cause the rotors to pitch towards rotor B2.

[85] As such, as can be appreciated, the platform 8 may be transition horizontally in 0°, 90°, 180° and 270° directions.

[86] However, the platform 8 may also be transition horizontally in minor angles in this manner. For example, so as to transition the platform 8 and a 45° direction, both pairs of radial arms would be rotated such that rotors Bl and B2 pitch forwards and rotors Al and A2 pitch rightwards (towards B2) to cause the platform 8 to travel in the 45° direction. [87] In travelling in these minor directions, the rotational angle of the arms 4 may be configured proportionate to the desired direction of travel. For example, to travel in a 15° direction, rotors Bl and B2 would be pitched at a greater angle as compared to rotors Al and A2. Similarly, to travel in a 80° direction, rotors Al and A2 would be pitched at a greater angle as compared to rotors Bl and B2.

[88] Turning now to figure 4, horizontal transition may similarly be achieved for other configurations such as for the hex copter 23.

[89] For example, to travel in a 0° direction, both rotor pairs Bl - B2 and CI - C2 would be pitched forwards such that the resultant thrust vector moves the platform 8 in the 0° direction.

[90] In embodiments, the angle of attack of the platform 8 may be configured during horizontal transitioning.

[91] Specifically, whereas as was described the platform being pitched forwards in accordance with conventional horizontal transition control, the present embodiments may allow for the selective adjustment of the pitch angle/angle of attack of the platform 8 while transitioning horizontally.

[92] For example, so as to minimise drag and downward forces on the platform 8 while transitioning horizontally, the platform 8 may be pitched substantially horizontally. Specifically, as can be appreciated, by controlling the rotational angle of the radial arms 4 in the manner described herein, the platform 8 need not be pitched forwards as per conventional arrangements.

[93] As such, the horizontal transition control of present embodiments allows the platform 8 to remain substantially horizontal so as to reduce wind drag and downward forces on the housing of the platform 8 thereby increasing efficiency.

[94] However, in embodiments, the flight controller 11 may even pitch the platform 8 at an upwards angle so as to generate hybrid lift across the undersurface of the platform 8, especially where the housing of the platform 8 is shaped aerodynamically.

[95] For example, with reference to figure 3, when transitioning in a 0° direction, the platform 8 may be pitched upwards (that is raised towards rotor Al and lowered towards rotor A2) so as to generate hybrid lift.

[96] Such pitch control may be achieved by the flight controller 11 controlling the respective throttles of rotors Al and A2. In this manner, the flight controller 11 simultaneously controls the rotating actuators of the radial arms 4 of rotors Bl and B2 to transition the quad copter 22 in the 0° direction and the throttles of the internal combustion engines 2 of rotors Al and A2 so as to adjust the pitch angle of the platform 8. In further embodiments, hybrid lift surfaces (as will be described in further detail below) may be utilised to control the angle of attack of the platform 8. [97] Of course, the roll angle may also be adjusted in this way including both the pitch and roll angle simultaneously, such as when travelling minor angle directions.

[98] In embodiments, hybrid lift may be achieved by way of additional flight surfaces. Specifically, turning to figure 5, there is shown in an embodiment of the quad copter 22 comprising a plurality of flight surfaces 9 fastened to the radial arms 4.

[99] In this manner, as the quad copter 22 transitions horizontally, the flight surfaces 22 may create additional lift, thereby increasing the efficiency of the quad copter 22.

[100] In embodiments, the flight surfaces 9 are fastened to the radial arms. However, in embodiments, the angle of the flight surfaces 9 may be controlled oppositely to that of the direction of rotation of the radial arms 4.

[101] For example, when travelling in a 0° direction, rotors Bl and B2 may be pitched forwards in the manner described above. However, to maintain the aerodynamic properties of the flight surfaces 9, the attack angles of the flight surfaces 9 corresponding to rotors Bl and B2 may be adjusted (i.e. to rotate about the elongate axis of the respective arm 4 in an opposite direction so as to pitch rearwards while the rotor pictures forwards) such that the flight surfaces 9 remain substantially horizontal or are even pitch rearwards.

[102] Mechanical linkages may interconnect each radial arm 4 and flight surface 9 such that a single actuator may be utilised to control both the rotation of the radial arm and the angle of the flight surface 9. As such, the mechanical linkage they cause the flight surface to pivot in an opposite direction to the rotational direction of the arm 4. In alternative embodiments, separate actuators may be utilised on each flight surface 9 being especially suited for where the pitch of the flight surfaces 9 is not proportional to the pitch of the associated rotor such as where, for example, the flight surfaces 9 is required to remain substantially horizontal as alluded to above.

[103] As also alluded to above, the flight surfaces 9 may be additionally utilised for controlling the pitch/angle of attack of the platform 8. Specifically, whereas the adjustment of the fore and aft throttle setpoints was described above for controlling the pitch of the platform 8, in additional or alternative embodiments, the flight surfaces 9 may be utilised in this manner.

[104] For example, with reference to figure 5, were the quad copter 22 travelling in a 0° direction and the direction of rotor Al, the flight control service 9 adjacent rotor Al may be rotated substantially vertically so as to effectively neutralise the lift generation thereof. Simultaneously, the rearward flight surface 9 may be left in place substantially horizontally so as to continue to generate lift thereby pitching the platform 8 forwards.

[105] In yet further embodiment, the fore flight surface 9 may even be configured to generate negative lift by rotation substantially through 180°. [106] Such control of the flight surfaces 9 to control the pitch of the platform 8 may also be utilised for the hex copter 23 configuration shown in figure 4.

[107] It is regard, while travelling in a 0° direction in the direction of rotor Al, the flight control 9 associated with rotor Al may be poised vertically so as to negate the lift generation thereof. Simultaneously, the flight surface 9 associated with rotor A2 may be left substantially horizontal so as to continue to generate positive lift so as to pitch the platform 8 forwards.

[108] Additionally, the flight surfaces 9 associated with rotor pairs and C may additionally be utilised in this manner. For example, the flight surfaces 9 associated with rotors Bl and C2 may be poised at substantially 45° so as to not entirely negate the lift generation thereof as is the case for the flight surface 9 of rotor Al. Furthermore, the poising of the flight surfaces 9 of Bl and C2 at opposing angles respectively may negate the lateral forces generated from the pitching of the flight surfaces 9 at this oblique angle.

[109] In this manner, the controller 11 may dynamically alter the pitch of the platform 8 in use through the selective operation of the flight surfaces 9 by rotating the flight surfaces 9 from horizontal to vertical poise is as is required.

[110] Turning now to figure 6, there is shown the flight controller 11 in further detail.

[Ill] The flight controller 11 may comprise firmware comprising a plurality of modules for implementing various functionality described herein. Alternatively, the flight controller 11 may execute software retrieved from memory device 16.

[112] As can be seen, the firmware 12 comprises a flight control module 13 configured to control various aspects of flight control, including that which is described herein. As such, the flight controller 13 may be configured for controlling the yaw, pitch, roll and horizontal transitioning of the platform 9 in the manner described herein.

[113] Now, internal combustion engines may be prone to failure for various reasons, such as lack of fuel, fuel contamination, fuel blockage, carburettor blockage and the like.

[114] As such, the firmware 12 may comprise an engine monitor 14 configured to monitor the operational status of each internal combustion engine 2.

[115] In alternative embodiments, an engine monitoring unit 14 may be provided for each internal combustion engine. Such an engine monitoring unit may itself comprise a processor configured to monitor the operational status of each internal combustion engine 2. Furthermore, each monitoring unit 14 may be located at a distal end of each arm 4 so as to be proximate each internal combustion engine 2. Yet further, each monitoring unit 14 may report measurements, calculations and the like to the main controller 11 and receive instructions therefrom 11. [116] Specifically, the engine monitor module/unit 14 may be configured to monitor the engine response in accordance with the throttle setpoint. Specifically, and as alluded to above, the controller 11 comprises a throttle controller which, in embodiments, may take the form of a pulse width modulator output 19 configured to control a throttle control 20 of each internal combustion engine 2. As such, by controlling the pulse width, the controller 11 may control the throttle setpoint for each internal combustion engine.

[117] So as to monitor the engine response to the throttle setpoint, the engine monitor module/unit 14 may be configured for monitoring the revolutions per minute of each internal combustion engine. In particular embodiment, a Hall effect transducer may detect a magnet mounted to the prop shaft of the internal combustion engine 2. The pulses from the Hall effect transducer 19 may be read by pulse input 17 of the controller 11.

[118] As such, the memory device 16 or engine monitoring unit 14 may be configured with various operational bounds indicative of normal performance. For example, each throttle setpoint may be associated with a minimum and maximum PM reading. As such, should the RPM deviate beyond these bounds, the controller 11 may detect impending engine failure.

[119] Furthermore, in embodiments, in addition to monitoring throttle setpoint response bounds, the engine monitoring module/unit 14 may be configured for monitoring the rate of change (derivative) of the engine response. For example, an internal combustion engine increasing speed too slowly may be indicative of impending engine failure.

[120] In this manner, the memory device 16/engine monitoring unit 14 may additionally comprise rate of change bounds such that should an engine respond with a rate of change exceeding these bounds, the controller 11 may detect engine failure.

[121] In embodiments, the engine monitoring module/unit 14 may monitor engine exhaust gas temperature, cylinder head temperature and vibration. A similar manner, seviation of these parameters from nominal values are detected by the engine monitoring module/unit 14 to detect impending engine failure.

[122] Now, normally the flight controller 13 may compensate for deviations in engine power output such as is monitored by various tilt, accelerometer sensors and the like. In this manner, the flight controller may correspondingly decrease power to an opposing rotor in the event of reduction in engine power.

[123] However, for internal combustion engines, even while the internal combustion engine is at the lowest throttle setpoint (idle) the lift generated by the internal combustion may be too great for the flight controller 13 to compensate for a total loss of power of the opposite internal combustion engine. [124] As such, the firmware 12 may comprise a failure recovery module 15 configured to address engine failure.

[125] For example, considering figure 3, it should rotor B2 cease to operate, the failure recovery module 15 may simultaneously cut power to the opposing rotor Bl such that the quad copter 22 flies by rotors Al and A2 alone.

[126] Similarly, and turning now to figure 4, a loss of power to rotor B2 may cause the failure recovery module 15 to cut or reduce power to opposing rotor Bl while rotors Al - A2 and CI - C2 remain operational.

[127] The failure recovery module 15 may thereafter implement recovery action, such as decreasing altitude, returning to base, deploying a parachute or drogue chute, notifying the operator and the like.

[128] In embodiments, the multirotor 1 may be configured for refuelling from a ground-based refuelling station. During refuelling, the multirotor 1 may remain airborne so as to suppress dust generation, maintain ground clearance and other performance and safety factor considerations.

[129] In this embodiment, the multirotor 1 may lower a proboscis to the refuelling station so as to receive fuel therefrom. In this regard, the refuelling station may comprise a pump to pump the fuel to a fuel tank of the multirotor 1. The pump of the refuelling station may pump fuel in accordance with pressure sensing or volumetric amount. In other embodiments, the multirotor 1 may monitor flowrate or fuel level so as to signal the refuelling station accordingly.

[130] In embodiments, communication between the multirotor 1 and the refuelling station may be along electrical conduits of the proboscis or alternatively wirelessly.

[131] Embodiments, the multirotor 1 may be permanently fixed to the refuelling station by way of a sufficient length of refuelling tubing been especially suited for long-term aerial surveillance.

Interpretation

Embodiments:

[132] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[133] Similarly it should be appreciated that in the above description of example embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description of Specific Embodiments are hereby expressly incorporated into this Detailed Description of Specific Embodiments, with each claim standing on its own as a separate embodiment of this invention.

[134] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

Different Instances of Objects

[135] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

Specific Details

[136] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. Terminology

[137] In describing the preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "forward", "rearward", "radially", "peripherally", "upwardly", "downwardly", and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

Comprising and Including

[138] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[139] Any one of the terms: including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

Scope of Invention

[140] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

[141] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Industrial Applicability

[142] It is apparent from the above, that the arrangements described are applicable to the multirotor industries.

Claims

1. A multirotor aircraft comprising:

a platform; and

at least two pairs of opposing radial arms extending from the platform, the radial arms supporting at least four internal combustion engine powered rotors;

rotating actuators for rotating each of the radial arms about an elongate axis; and a flight controller configured for controlling the rotating actuators, wherein:

the rotors rotate in the same direction; and

the flight controller is configured for yaw control by controlling the rotating actuators to rotate at least one pair of the opposing radial arms in opposing rotational directions.

2. A multirotor aircraft as claimed in claim 1, wherein the flight controller is configured for yaw control by controlling the rotating actuators to rotate at least two pairs of the opposing radial arms in opposing rotational directions.

3. A multirotor aircraft as claimed in claim 1, wherein the flight controller is configured for horizontal transition control by controlling the rotating actuators to rotate at least one pairs of the opposing radial arms in the same rotational directions.

4. A multirotor aircraft as claimed in claim 2, wherein the flight controller is configured for horizontal transition control by controlling the rotating actuators to rotate at least two pairs of the opposing radial arms in the same rotational directions.

5. A multirotor aircraft as claimed in claim 1, wherein the flight controller is configured for horizontal transition control by controlling the rotating actuators to rotate each of the at least two pairs of the opposing radial arms to differing rotational offsets.

6. A multirotor aircraft as claimed in claim 5, wherein the differing rotational offsets are determined by the flight controller in accordance with a desired direction of travel.

7. A multirotor aircraft as claimed in claim 5, wherein the at least two pairs of opposing radial arms are three pairs of radial arms.

8. A multirotor aircraft as claimed in claim 5, wherein the at least two pairs of opposing radial arms are four pairs of radial arms.

9. A multirotor aircraft as claimed in claim 5, wherein the flight controller is further configured for controlling throttles for each rotor and wherein the flight controller is configured for roll and pitch control by controlling throttle setpoints of opposing rotors of at least one pair of the radial arms.

10. A multirotor aircraft as claimed in claim 5, wherein the flight controller is configured for roll and pitch control by controlling throttle setpoints of opposing rotors of at least two pairs of the radial arms.

11. A multirotor aircraft as claimed in claim 1, further comprising at least one flight surface operably coupled to an associated arm.

12. A multirotor aircraft as claimed in claim 11, further comprising an actuator for adjusting the pitch of the flight surface about the elongate axis of the arm.

13. A multirotor aircraft as claimed in claim 12, wherein the flight controller is configured for adjusting the pitch of the flight surface.

14. A multirotor aircraft as claimed in claim 13, wherein each flight surface has a corresponding mechanical linkage to the respective radial arm to pitch the flight surface.

15. A multirotor aircraft as claimed in claim 5, wherein the flight controller is further configured for controlling the pitch of the platform in a direction of travel.

16. A multirotor aircraft as claimed in claim 15, wherein the flight controller is configured for controlling the pitch of the platform by controlling a throttle setpoint of at least one of fore and aft rotors.

17. A multirotor aircraft as claimed in claim 15, further comprising flight surfaces operably coupled to each arm, each flight surfaces having an associated actuator for pitching the flight surface about the elongate axis of the associated arm and for being controlled by the controller and wherein the flight controller is configured for controlling the pitch of the platform by controlling the pitch of at least one of the flight surfaces.

18. A multirotor aircraft as claimed in claim 15, wherein the flight controller is configured for controlling the pitch of the platform by pitching a fore flight surfaces substantially vertically so as to reduce lift generated by the fore flight surfaces.

19. A multirotor aircraft as claimed in claim 15, wherein the flight controller is configured for controlling the pitch of the platform by pitching an aft flight surfaces substantially horizontally so as to maintain lift generated by the aft flight surfaces.

20. A multirotor aircraft as claimed in claim 5, wherein the flight controller is configured for engine failure monitoring.

21. A multirotor aircraft as claimed in claim 20, wherein engine failure monitoring comprises monitoring an engine response to a throttle setpoint.

22. A multirotor aircraft as claimed in claim 21, wherein monitoring the engine response comprises monitoring the revolution speed of a propeller shaft of each internal combustion engine.

23. A multirotor aircraft as claimed in claim 22, wherein monitoring the engine response comprises determining whether the revolution speed falls within a bound specified for a particular throttle setpoint.

24. A multirotor aircraft as claimed in claim 22, wherein monitoring the engine response comprises determining the rate of change of the revolution speed.

25. A multirotor aircraft as claimed in claim 24, wherein monitoring the engine response comprises determining whether the rate of change of the revolution speed falls within rate of change bounds.

26. A multirotor aircraft as claimed in claim 20, wherein engine failure monitoring comprises detecting an engine failure and controlling a throttle setpoint of an opposing rotor.

27. A multirotor aircraft as claimed in claim 20, wherein engine failure monitoring comprises monitoring at least one of cylinder head operating temperatures and exhaust gas temperatures.

28. A multirotor aircraft as claimed in claim 20, wherein engine failure monitoring comprises monitoring engine vibration levels.